This application claims the priority of German patent document 199 33 321.1, filed Jul. 16, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for permitting stable operation of a vehicle at an extremely low vehicle speed.
Most all-wheel or cross-country vehicles for use in extreme terrain have an additional transmission position for a so-called xe2x80x9clowxe2x80x9d operating mode in which it is possible to drive the vehicle at extremely low speeds in difficult terrain. Frequently, this transmission position can be switched on and off only when the vehicle is stopped. The provision of such an additional transmission position requires substantial technical expenditures, space and increases in weight.
It is an object of the invention to provide an improved method and apparatus of the initially mentioned type in which cost and weight are minimized, and the handling is simplified.
This and other objects and advantages are achieved by the method and apparatus according to the invention, in which an engine electronic control unit enables a special engine speed either automatically or in response to the occurrence of a predetermined set of vehicle operating parameters. The special engine speed, which is lower than that which is permitted under normal operating conditions, can be sustained for a limited period of time, without impairment of vehicle operation.
In a first alternative according to the invention, while a designated switch is actuated manually (either a specially provided switch or an existing multifunction switch), the internal-combustion is adjusted to a special rotational speed operation by the electronic control unit using known engine control techniques. During such special rotational speed operation, the electronic control unit permits the engine to operate at a special rotational speed that is below the normally permitted idling rotational speed.
In a second alternative, when a defined condition of the internal-combustion engine exists, the control unit automatically adjusts the internal-combustion engine to a special rotational speed operation, during which the special rotational speed is below the normally defined idling rotational speed. Respective defined conditions for such automatic implementation may be, for example:
Sensors connected with the control unit detect that the vehicle speed is below a defined threshold; and/or
sensors connected with the control unit detect that the 1st gear or the reverse gear is used; and/or
sensors connected with the control unit detect extreme unevennesses of the road; and
sensors connected with the control unit detect extreme longitudinal and/or transverse slopes; and or
sensors connected with the control unit detect a trailer operation, a parking operation or an extreme stop-and-go operation, etc.
The special rotational speed operation is preferably set only for a predetermined time period, after which it is automatically switched off. Alternatively, after a predetermined time period, a recommendation or signal (acoustic, optic or haptic) can be emitted to the driver. In the latter case, if the predetermined time period has expired and/or the driver does not follow the recommendation for a relatively long time, the special rotational speed operation can subsequently be switched off automatically.
As a further development of the invention, the special rotational speed operation is switched on and/or off as a function of rotational-speed relevant operating conditions.
Idling rotational speed is normally set so that operating considerations which do not directly affect the internal-combustion engine but are rotational-speed relevant, such as a switched-on air conditioner, battery charging, acoustics, etc. can be maintained optimally. A reduction of the rotational speed of the internal-combustion engine to an extremely low special rotational speed below the idling rotational speed cannot therefore not be set for all operating conditions and/or can be set only for a limited time.
In another advantageous further embodiment of the invention, as an alternative (or in addition), the switched-on special rotational operation is automatically switched off during gear shifting operations, for example, upshifting from the 1st gear or the transition from the reverse gear into the neutral position.
In another advantageous further development of the invention, as an alternative or in addition, the switched-on special rotational speed operation is automatically switched off when a defined vehicle speed is exceeded.
All alternatives can also be combined with one another.
In addition, a switching-off of the special rotational speed operation can also always take place manually by the driver, for example, by operating the switch intended for this purpose.
The switchover to special rotational speed operation, or out of the special rotational speed operation, need not take place only when the vehicle is stopped, as in the known systems, but can also take place during driving.
As a result of the invention, no additional transmission position is required. Rather, an extremely low driving speed for special driving situations (for example, in difficult terrain) is achieved by situation-related activation of a targeted reduction of the rotational speed of the internal-combustion engine via the engine electronic control unit, which exists in all events, for other engine control purposes.
Nowadays, modern electronically controlled internal combustion engines can be operated, for at least a limited time, at extremely low rotational speeds in a stable manner (that is, without a bucking and without a stalling of the internal-combustion engine). Higher idling rotational speeds are often dictated by rotational-speed-dependent values (air conditioner, battery charging condition, acoustics). For a time-limited driving condition, however, these values can be neglected in order to reach extreme vehicle speeds. This operational adaptation can take place without a slipping clutch, thus without any thermal overloading of clutch or transmission parts.
The invention is not limited to cross-country vehicles. It can also be used for improving the driving and the parking maneuvers, for example, during an extreme uphill or downhill drive and/or during a trailer operation and/or during a difficult parking maneuver and/or in the stop-and-go operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.